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A stick of cordite from World War II.
A sectioned British 18 pounder field gun shrapnel round, World War I, showing string bound to roughly simulate the appearance of the cordite propellant
Sticks of cordite from a .303 British rifle cartridge.

Cordite is a family of smokeless propellants developed and produced in the United Kingdom from 1889 to replace gunpowder as a military propellant. Like gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance. These produce a subsonic deflagration wave rather than the supersonic detonation wave produced by brisants, or high explosives. The hot gases produced by burning gunpowder or cordite generate sufficient pressure to propel a bullet or shell to its target, but not enough to destroy the barrel of the firearm, or gun.

Cordite was used initially in the .303 British, Mark I and II, standard rifle cartridge between 1891 and 1915; however shortages of cordite in World War I led to United States-developed smokeless powders being imported into the UK for use in rifle cartridges. Cordite was also used for large weapons, such as tank guns, artillery and naval guns. It has been used mainly for this purpose since the beginning of World War I by the UK and British Commonwealth countries. Its use was further developed in the early years of World War II, as 2-inch and 3-inch diameter Unrotated Projectiles for launching anti-aircraft weapons.[1] Small cordite rocket charges were also developed for ejector seats made by the Martin-Baker Company.

Cordite is now obsolete and it is no longer produced. It has been replaced by other propellants, such as the Improved Military Rifle (IMR) line of extruded powder or the WC844 ball propellant currently in use in the 5.56x45mm NATO.[2 ] Production ceased in the United Kingdom, around the end of the 20th century, with the closure of the last of the World War II cordite factories, ROF Bishopton. However, cordite propellant may still be encountered in the form of legacy ammunition dating from World War II onwards. The smell of cordite is frequently referenced (erroneously) in fiction to indicate the recent firing of weapons.

Contents

Adoption of smokeless powder by the British government

Replacements for gunpowder (black powder)

Gunpowder, an explosive mixture of sulfur, charcoal and potassium nitrate (also known as saltpetre/saltpeter), was the original gun propellant employed in firearms and fireworks. It was used from about 10th or 11th century onwards, but had a number of disadvantages. With the 19th century development of various "nitro explosives", based on the reaction of nitric acid mixtures on materials such as cellulose and glycerine, a search began for a replacement for gunpowder.

Early European smokeless powders

The first smokeless powder, Poudre B, was developed in 1884 by the French chemist Paul Vieille. It was made out of two forms of nitrocellulose (collodion and guncotton) softened with ethanol and ether and kneaded together. It was immediately adopted by the French military but it tended to become unstable over time. The rifle and cartridge developed to utilize this powder were known generically as the '8 mm Lebel', after the officer in charge of the development board, and were fielded in 1886.

The following year, 1887, Alfred Nobel invented and patented a smokeless propellant he called Ballistite. It was composed of 10% camphor, 45% nitroglycerine and 45% collodion (nitrocellulose). Over time the camphor tended to evaporate, leaving an unstable explosive.

Development of cordite

A United Kingdom government committee, known as the "Explosives Committee", chaired by Sir Frederick Abel, monitored foreign developments in explosives and obtained samples of Poudre B and Ballistite. However, neither of these smokeless powders were recommended for adoption by the Explosives Committee.

Abel and Sir James Dewar, who was also on the committee, developed and jointly patented in 1889 a new propellant consisting of 58% nitroglycerine, by weight, 37% guncotton and 5% vaseline. Using acetone as a solvent, it was extruded as spaghetti-like rods initially called "cord powder" or "the Committee's modification of Ballistite" but this was swiftly abbreviated to "Cordite".

Cordite began as a double-base propellant and later triple-base cordites were developed. Cordite was made by combining two high explosives: nitrocellulose and nitroglycerine. Whilst cordite is classified as an explosive, it is not employed as a high explosive. It is designed to deflagrate, or burn, to produce high pressure gases.

Nobel and Abel patent dispute

Alfred Bernhard Nobel sued Abel and Dewar over an alleged patent infringement. His patent specified that the nitrocellulose should be "of the well-known soluble kind". After losing the case it went to the Court of Appeal. This dispute eventually reached the House of Lords, in 1895, but was finally lost because the words "of the well-known soluble kind" in his patent were taken to mean the soluble collodion and hence specifically excluded the insoluble guncotton.[3] The ambiguous phrase was "soluble nitro-cellulose": soluble nitro-cellulose was known as Collodion and was soluble in alcohol. It was employed mainly for medical and photographic use. In contrast, insoluble, in alcohol, nitrocellulose was known as gun cotton and was used as an explosive.[3][4] Nobel's patent refers to the production of Celluloid using camphor and soluble nitrocellulose; and this was taken to imply that Nobel was specifically distinguishing between the use of soluble and insoluble nitrocellulose.[4]

Cordite formulations

It was quickly discovered that the rate of burning could be varied by altering the surface area of the cordite. Narrow rods were used in small-arms and gave relatively fast burning, while thicker rods would burn more slowly and were used for longer barrels such as those used in artillery and naval guns.

Cordite (Mk I) and Cordite MD

The original Abel-Dewar formulation was soon superseded as it caused excessive gun barrel erosion. It has since become known as Cordite Mk I.

The composition of cordite was changed to 65% guncotton and 30% nitroglycerine (keeping 5% vaseline) shortly after the end of the Second Boer War. This was known as Cordite MD (= MoDified).

Cordite MD cartridges typically weighed approximately 15% more than the cordite Mk I cartridges they replaced, to achieve the same muzzle velocity, due to the inherently less powerful nature of Cordite MD.[5]

Cordite MD is now obsolete.

Cordite RDB

During World War I acetone was in short supply in Great Britain and a new experimental form was developed.[6] This was Cordite RDB (= Research Department formula B); which was 52% collodion, 42% nitroglycerine and 6% Vaseline (petroleum jelly). It was produced at HM Factory, Gretna;[6] and the Royal Navy Cordite Factory, Holton Heath.

Cordite RDB, unfortunately, tended to become unstable if stored too long. Once acetone production increased, by the use of fermentation (see Chaim Weizmann), the older form of cordite, Cordite MD, was brought back for use by the Royal Navy.

Cordite SC

Research on solvent-free Cordite RDB continued primarily on the addition of stabilizers, which led to the type commonly used in World War II onwards. In Great Britain this was known as Cordite SC (= Solventless Cordite). Cordite SC was produced in different shapes and sizes so the particular geometry of Cordite SC was indicated by the use of letters or numbers, or both, after the SC. For example SC followed by a number was rod-shaped cord, with the number representing the diameter in thou. "SC T" followed by two sets of numbers indicated tubular propellant with the numbers representing the two diameters in thou.

Two-inch (approximately 50 mm) and three-inch (approximately 75 mm) diameter, Unrotated Projectiles, rocket Cordite SC charges were developed in great secrecy in the later stages of WW II for anti-aircraft purposes—the so-called Z-gun batteries.[1]

Great Britain changed to metric units in the 1960s so there was a discontinuity in the propellant geometry numbering system.

Cordite N

An important development during World War II was the addition of another explosive, nitroguanidine, to the mixture to form triple-base propellant or Cordite N. This solved two problems with the large naval guns of the day as fitted to capital ships. Nitroguanidine produces large amounts of nitrogen when heated, which had the benefit of reducing the muzzle flash and its lower burning temperature greatly reduced the erosion of the gun barrel.

Cordite charge design

Cordite manufacture

UK Government factories

In Great Britain cordite was developed for military use at the Royal Arsenal, Woolwich, and at the Waltham Abbey Royal Gunpowder Mills from 1889 onwards.

In World War I a great cordite factory, HM Factory, Gretna, which straddled the Scotland-England border at Gretna was opened to manufacture cordite for the British Army and for British Commonwealth forces. A separate factory, The Royal Navy Cordite Factory, Holton Heath, was opened to manufacture cordite for the Royal Navy. Both the Gretna and the Holton Heath cordite factories closed at the end of World War I; and the Gretna factory was demolished.

By the start of World War II Holton Heath had reopened and an additional factory for the Royal Navy, The Royal Navy Propellant Factory, Caerwent, opened at Caerwent in Wales. A very large Royal Ordnance Factory, ROF Bishopton, was opened in Scotland to manufacture cordite for the British Army and the Royal Air Force. A new cordite factory at Waltham Abbey and two additional ROF's—ROF Ranskill and ROF Wrexham—were also opened. Cordite produced in these factories was sent to Filling Factories for filling into ammunition.

MoS Agency Factories and ICI Nobel in World War II

The British Government set up additional cordite factories, not under Royal Ordnance Factory control but as Agency Factories run on behalf of the Ministry of Supply (MoS). The company of ICI Nobel, at Ardeer, was asked in 1939 to construct and operate six factories in southern Scotland. Four of these six were involved in cordite or firearm-propellant manufacture. The works at MoS Drungans (Dumfries) produced guncotton that was converted to cordite at MoS Dalbeattie (triple-base cordite) and at MoS Powfoot (monobase granulated guncotton for small-arms). A smaller site at Girvan,South Ayrshire, now occupied by Grant's distillery, produced cordite and TNT.[7] The ICI Ardeer site also had a mothballed World War I Government-owned cordite factory.[8]

35% of British cordite produced between 1942 and 1945 came from Ardeer and these agency factories.[9] ICI ran a similar works at Deer Park near Melbourne in Australia and in South Africa.[9]

Overseas supplies

Additional sources of propellant were also sought from the British Commonwealth in both World War I and World War II. Canada, South Africa and Australia, had ICI-owned factories that, in particular, supplied large quantities of cordite.

World War I

Canadian Explosives Limited was formed in 1910 to produce rifle cordite, at its Beloeil factory, for the Quebec Arsenal. By November 1915 production had been expanded to produce 350,000 lb (159,000 kg) of cordite per month for the Imperial Munitions Board.[10]

The Imperial Munitions Board set up a number of additional explosives factories in Canada. It built The British Cordite Ltd factory at Nobel, Ontario, in 1916/1917, to produce cordite. Production started in mid 1917.[10]

Canadian Explosives Limited built an additional cordite factory at Nobel, Ontario. Work stated in February 1918 and was finished on 24 August 1918. It was designed to produce 1,500,000 lb (681,000 kg) of cordite per month.[10]

World War II

The United States did not use cordite, however, several ammunition filling factories were set up in Canada in World War II to fill American propellant supplied by the USA under Lend-Lease. India, Pakistan and Australia were also approached. Cordite was used in "Little Boy", the atomic bomb dropped on Hiroshima, Japan during World War II. A modified anti-aircraft cannon barrel using cordite fired one subcritical piece of U-235 together with another to form a supercritical mass.

Production quantities

Large quantities of cordite were manufactured in both World Wars for use by the military.

Pre-World War I

Prior to World War I, most of the cordite used by the British Government was produced in its own factories. Immediately prior to World War I, between 6,000 and 8,000 tons per year of cordite were produced in the United Kingdom by private manufacturers; between 1,000 and 1,500 tons per year were made by Nobel's Explosives, at Ardeer.[8] However, private industry had the capability to produce about 10,000 tons per year, with Ardeer able to produce some 3,000 tons of this total.[8]

World War I

At the start of World War I, private industry in the UK was asked to produce 16,000 tons of cordite, and all the companies started to expand.[8] HM Factory, Gretna, the largest propellant factory in the United Kingdom, which opened in 1916, was by 1917 producing 800 tons (812 tonne) of Cordite RDB per week (approximately 41,600 tons per year).[6][8] The Royal Navy had its own factory at Holton Heath.

In 1910, Canadian Explosives Limited produced 3,000 lb (1,362 kg) of rifle cordite per month at its Beloeil factory, for the Quebec Arsenal. By November 1915 production had been expanded to 350,000 lb (159,000 kg) of cordite per month (approximately 1,900 tonnes per year).[10] The Canadian Explosives Limited cordite factory at Nobel, Ontario was designed to produce 1,500,000 lb (681 tonne) of cordite per month (approximately 8,170 tonnes per year).

Between wars

HM Factory, Gretna and the Royal Navy Cordite Factory, Holton Heath both closed after the end of the war and the Gretna factory was dismantled.[6] This left the Waltham Abbey and Ardeer factories in production.

References

Notes

  1. ^ a b Brown 1999, Chapter 17
  2. ^ Watters, Daniel, "The Great Propellant Controversy", The Gun Zone, http://www.thegunzone.com/556prop.html, retrieved 2009-11-30  
  3. ^ a b Schuck & Sohlman 1929, pp. 136-144
  4. ^ a b Schuck & Sohlman 1929, Appendix I: Alfred Nobel's English lawsuit. Mr justice Romer's judgment in the "Cordite Case"
  5. ^ Example : BL 6-inch Mk VII gun : 20 lb cordite Mk I, 23 lb cordite MD. Table 8 in Treatise on Ammunition 1915.
  6. ^ a b c d Ministry of Munitions of War
  7. ^ Cocroft 2000, Gazetteer
  8. ^ a b c d e Reader 1975, Chapter 14: "Warlike Supply"
  9. ^ a b Reader 1975, Chapter 15: "War Production"
  10. ^ a b c d Carnegie (1925).

Bibliography

  • Bowditch, M.R.; Hayward, L. (1996). A Pictorial record of the Royal Naval Cordite Factory: Holton Heath. Wareham:: Finial Publishing. ISBN 1-900467-01-1.  
  • Brown, Donald (1999). Somerset v Hitler: Secret Operations in the Mendips 1939 - 1945. Newbury: Countryside Books. ISBN 1-85306-590-0.  
  • Carnegie, David (1925). The History of Munitions Supply in Canada 1914-1918. London: Longmans, Green and Co.  
  • Cocroft, Wayne D. (2000). Dangerous Energy: The archaeology of gunpowder and military explosives manufacture. Swindon: English Heritage. ISBN 1-85074-718-0.  
  • Davis, Tenney L. (1943). The Chemistry of Powder and Explosives. Volume II. New York: John Wiley & Sons.  
  • Hartcup, Guy (1970). The Challenge of War: Scientific and Engineering Contributions to World War Two. Newton Abbot:: David & Charles. ISBN 0-7153-4789-6.  
  • Reader, W.J. (1975). Imperial Chemical Industries: A History. Volume II; The First Quarter-Century 1926-1952. London: Oxford University Press. ISBN 0-19-215944-5.  
  • Schuck, H.; Sohlman, R. (1929). The Life of Alfred Nobel. London: William Heinemann.  
  • Ministry of Munitions of War (1919). H.M. Factory, Gretna: Description of plant and process. Dumfries: J. Maxwell and Son, for His Majesty's Stationery Office.  
  • Rotter, Andrew J. (2008). Hiroshima: The World's Bomb. Oxford: Oxford University Press.  

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

CORDITE, the name given to the smokeless propellant in use in the British army and navy. The material is produced in the form of cylindrical rods or strings of varying thicknesses by pressing the material, whilst in a soft and pasty state, through dies or perforations in a steel plate by hydraulic or screw pressure, hence the name cordite. The thickness or size of the rods varies from about 1 mm. diameter to 5 or more mm. according to the nature of the charge for which it is intended. The smallest diameter is used for revolver cartridge and the largest for heavy guns. When first devised by the Ordnance Committee, presided over by Sir Frederick Abel, in 1891, this explosive consisted of 58% of nitro-glycerin, 37% of gun-cotton, and 5% of mineral jelly. This variety is now known as Cordite Mark I. At the present time a modification is made which contains gun-cotton 65%, nitro-glycerin 30%, and mineral jelly 5%. This is known as Cordite M.D. The advantages of Cordite M.D. over Mark I are slightly reduced rate of burning, higher velocities and more regular pressure in the gun, and lower temperature.

Cordite of either mark is a perfectly waterproof substance, containing only traces of water remaining from the manufacturing processes. It has a density of about 1.56 at the ordinary temperature (15° C.), and, as its coefficient of expansion is small, this density does not change to any serious extent under climatic temperature variations. A rod may be bent to a moderate extent without breaking, and Cordite M.D. especially shows considerable elasticity. It can be impressed by the nail and cut with a knife, but is not in the least sticky, nor does the nitroglycerin exude to any appreciable extent. It can be obtained in a finely-divided state by scraping with a sharp knife, or on a new file, or by grinding in a mill, such as a coffee-mill, but can scarcely be pounded in a mortar. Cordite is of a brownish colour in mass, but is much paler when finely ground or scraped. The rods easily become electrified by gentle friction with a dry substance. Like all colloidal substances it is an exceedingly bad conductor of heat. A piece ignited in air burns with a yellowish flame. With the smaller sizes, about 2 mm. diameter or less, this flame may be blown out, and the rod will continue to burn in a suppressed manner without actual flame, fumes containing oxides of nitrogen being emitted. Temperature appears to have an effect on the rate of burning. When much cooled it certainly burns more slowly than when at the ordinary air temperature, and is also more difficult to ignite. Rods of moderate thickness, say from 5 mm. diameter, will continue to burn under water if first ignited in air and the burning portion slowly immersed. The end of a rod of cordite may be struck a moderately heavy blow on an anvil without exploding or igniting. The rod will first flatten out. A sharp blow will then detonate or explode the portion immediately under the hammer, the remainder of the rod remaining quite intact. Bullets may be fired through a bundle or package of cordite without detonating or inflaming it. This is of course a valuable quality. The exact temperature at which substances ignite or take fire is in all cases difficult to determine with any exactness. Cordite is not instantly ignited on contact with a flame such as that of a candle, because, perhaps, of the condensation of some moisture from the products of burning of the candle upon it. A blow-pipe flame or a red-hot wire is more rapid in action. The ignition temperature may be somewhere in the region of 180° C.

All the members of this class of explosive when kept for some time at (for them) moderately high temperatures, such as the boiling-point of water (zoo° C.), show signs of decomposition; oxides of nitrogen are liberated, and some complex oxidation processes are started. Carefully prepared gun-cotton and nitroglycerin will, however, withstand this temperature for a long time without serious detriment, excepting that nitro-glycerin is slightly volatilized. When incorporated in cordite, however, the nitro-glycerin appears to be much less volatile than when free at this temperature. Under reduced pressure (3 or 4 in. only of mercury instead of 30) it is possible to distil away a considerable amount of nitro-glycerin from cordite at ioo° C. It is very doubtful whether at ordinary temperatures and pressures any nitro-glycerin whatever evaporates.

Cordite may be kept in contact with clean, dry metals, wood, paper, and a number of ordinary substances without deterioration. In contact with damp and easily oxidizable metals all the substances of the gun-cotton class are liable to a slight local action, but the colloid nature, and probably also the contained mineral jelly, protect cordite considerably in these circumstances. Ammonia has a deleterious action, but even this proceeds but slowly. Cordite does not appear to change when kept under water.

The manufacturing processes comprise: drying the guncotton and nitro-glycerin; melting and filtering the mineral jelly; weighing and mixing the nitro-glycerin with the gun-cotton; moistening this mixture with acetone until it becomes a jelly; and then incorporating in a special mixing mill for about three hours, after which the weighed amount of mineral jelly is added and the incorporation continued for about one hour or until judged complete. The incorporating or mixing machine is covered as closely as possible to prevent too great evaporation of the very volatile acetone. Before complete incorporation the mixture is termed, in the works, "paste," and, when finally mixed, "dough." The right consistency having been produced, the material is placed in a steel cylinder provided with an arrangement of dies or holes of regulated size at one end, and a piston or plunger at the other. The plunger is worked either by hydraulic power or by a screw (driven from ordinary shafting). Before reaching and passing through the holes in the die, the material is filtered through a disk of fine wire gauze to retain any foreign substances, such as sand, bits of wood or metal, or unchanged fibres of cellulose, &c., which might choke the dies or be otherwise dangerous. The material issues from the cylinders in the form of cord or string of the diameter of the holes of the die. The thicker sizes are cut off, as they issue, into lengths (of about 3 ft.), it being generally arranged that a certain number of these - say ten - should have, within narrow limits, a definite weight. The small sizes, such as those employed for rifle cartridges, are wound on reels or drums, as the material issues from the press cylinders, in lengths of many yards.

Some of the solvent or gelatinizing material (acetone) is lost during the incorporating, and more during the pressing process and the necessary handling, but much still remains in the cordite at this stage. It is now dried in heated rooms, where it is generally spread out on shelves, a current of air passing through carrying the acetone vapour with it. In the more modern works this air current is drawn, finally, through a solution of a substance such as sodium bisulphite; a fixed compound is thus formed with the acetone, which by suitable treatment may be recovered. The time taken in the drying varies with the thickness of the cordite from a few days to several weeks. For several reasons it is desirable that this process should go on gradually and slowly.

After drying, all the various batches of cordite of the same size are carefully "blended," so that any slight differences in the manufacture of one batch or one day's output may be equalized as much as possible. Slight differences may arise from the raw materials, cotton waste or glycerin, or in the making of these into gun-cotton or nitro-glycerin respectively. To help in controlling the blending, each "make" of gun-cotton and nitroglycerin is "marked" or numbered, and carries its mark to the cordite batch of which it is an ingredient. The history of each box of large-sized or reel of small-sized cordite is therefore known up to the operation of blending and packing. The final testing is by firing proofs, as in the case of the old gunpowders.

The gun-cotton employed for cordite is made in the usual way (see GUN-Cotton), with the exception of treating with alkali. It is also after complete washing with water gently pressed into small cylinders (about 3 in. diameter and 4 in. high) whilst wet, and these are carefully dried before the nitro-glycerin is added. The pressure applied is only sufficient to make the gun-cotton just hold together so that it is easily mixed with the nitro-glycerin. The mineral jelly or vaseline is obtained at a certain stage of distillation of petroleum, and is a mixture of hydrocarbons, paraffins, olefines and some other unsaturated hydrocarbons, possibly aromatic, which no doubt play a very important part as preservatives in cordite.

The stability of cordite, that is, its capability of keeping without chemical or ballistic changes, is judged of by certain "heat tests." The Abel heat test consists in subjecting a weighed quantity, 2 grams, of the finely divided cordite contained in a test tube, to a temperature of 70° C. maintained constant by a water bath. The test tube is about 6X4 in., and dips into the water sufficiently to immerse about 2 in., viz. the part containing the cordite. In the upper free portion a piece of filter-paper impregnated with a mixture of potassium iodide and starch paste is suspended by a platinum wire from the stopper of the tube. A portion of the test paper is moistened with a solution of glycerin to render it more sensitive than the dry part. A faint brown colour appearing on the moistened portion indicates that some oxides of nitrogen have been evolved from the cordite. This brown tint is compared with a standard, and the time taken before the standard tint appears is noted. The time fixed upon as a test of relative stability is an arbitrary one determined by examination of well-known specimens. Should the cordite or other explosive contain traces of mercury salts, such as mercuric chloride, which is sometimes added as a preservative, this test is rendered nugatory, and no coloration may appear (or only after a long exposure), although the sample may be of indifferent stability. It is now customary to examine specially for mercury, either by heating the explosive in contact with gold leaf or silver foil, or by burning the substance and examining the flame in the spectroscope.

The method of examination known as the vacuum silvered vessel process is probably not interfered with by the presence of very small quantities of mercury. It consists in heating s o grams of the finely divided explosive in a Dewar's silvered vacuum glass bulb to a rigidly constant temperature of 80° C. for many hours. A sensitive thermometer having its bulb immersed in the centre of the cordite shows when the temperature rises above 80°. Stich a rise indicates internal oxidation or decomposition of the explosive; it is accompanied by an evolution of nitrogen dioxide, N02, the depth of colour of which is noted through a side tube attached to the bulb: As all explosives of this class would in time decompose sufficiently to give these indications, time periods or limits have been fixed at which an appreciable and definite rise in temperature and production of red fumes indicate relative stability or instability. (W. R. E. H.)


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